Apparatus for developing electrostatic images of records



May 9, 1967 ToKu HOJO ETAL APPARATUS FOR DEVELOPING ELECTROSTATIC IMAGESOF RECORDS Filed Jan. 27, 1965 S 0' come/fa n m w Mi w IHW f mm 5 UnitedStates Patent f 3,318,284 APPARATUS FOR DEVELOPING ELECTROSTATIC IMAGESOF RECORDS Toku Hojo and Motoji Matsuda, Yokohama-sin, Japan, assignorsto Hitachi, Ltd., Tokyo, Japan, a corporation of Japan Filed Jan. 27,1965, Ser. No. 428,455 Claims priority, application Japan, Jan. 30,1964,

- 39/ 4,266 7 Claims. (Cl. 118637) This invention relates to apparatusfor developing electrostatic images of records.

A method of developing electrostatic latent images of records by use ofpowder ink is shown, which is called magnetic brush method, and in whicha recording carrier surface having electrostatic latent images impartedthereon is swept by a so-called magnetic brush thereby to develop thelatent images, which brush is formed by a magnet having a mixture inappropriate proportion of magnetic powder called carrier andthermofusible, colored-powder ink called toner, adsorbed by the magnetin a brush-like manner. In such a known method, the amount ofelectrostatic charge as well as the concentration of the toner are veryuneven and unstable, and yet, its contact with electrostatic latentimages can hardly be uniform. As a result, the concentration ofdeveloped images is not uniform with unnecessary fogging contaminationformed. Particularly, in case of wide and long web of recording carrieror plural sheets are developed at high speed, the concentration of toneris more difficult to control, resulting in very uneven development andgrazing, with concentration difference of development to a great extentbetween the beginning and ending portions of development. If tonershould additionally be fed midway in order to compensate for suchdefault, its commingling with carrier and charging would not be effectedsufliciently, and excess free toner attaches to the outer end ofmagnetic brush, resulting in extraordinary fogging contamination.

An object of the present invention is to provide an apparatus fordeveloping electrostatic latent images formed by electrophotography orother methods of recording by means of electrostatic charging, by use ofpowder ink, particularly adapted for the cases of long web of recordingcarrier and plural sheets of recording carriers jointly dealt with.

Another object of the present invention is to provide a compact andeconomical magnetic brush in the apparatus above-specified, with apermanent magnet having such shape and arrangement that its magneticfield is most effective, and has the most suitable length andflexibility for developing.

Another object of the present invention is to provide the apparatusabove-specified, in which a stirring brush formed by strong metal wiresplanted on and insulated from a rotating shaft is associated with themagnetic brush in deep intersection, and immersed mostly into thedeveloping agent of mixed carrier and toner in a reservoir for utilizingits commingling, charging, carrying and combining effects, whereby toneron the magnetic brush being consumed in the developing is effectivelysupplemented for keeping the amount of charge and concentration of tonerheld by the magnetic brush within the required range, and at the sametime, for maintaining the magnetic brush in uniform combining andflexible condition to sweep the surface of electrostatic latent imagesin the best condition.

A further object of the present invention is to provide the apparatusabove-specified, in which the consumption of toner of the developingagent in a reservoir can be supplemented at a suitable rate from anassociated toner 3,318,284 Patented May 9, 1967 storeroom havingstirring and feeding brush, intermittently or continuously.

A still further object of the present invention is to provide theapparatus above-specified, in which the concentration of toner held bythe magnetic brush may be detected when required, for controlling therotating speed of magnetic brush to obtain the best result ofdevelopment,

whereby clear and homogeneous development can be effected with leastfogging contamination.

There are other objects and particularities of the present invention,which will be made obvious from the following detailed description ofthe invention, with reference to the accompanying drawings, in which;

FIG. 1 is a sectional side view of the essential portion of an apparatusembodying the present invention; and

FIG. 2 is a block diagram of the speed control system for the magneticbrush shown in FIG. 1.

Referring to FIG. 1, the apparatus shown comprises a pair of magneticbrushes, each consisting of a plurality of permanent magnets 1 of largecoercive magnetic force, secured to respective side faces of apolygonal, say hexagonal, non-magnetic supporter bar 3 with equalspacings, with the same poles placed in opposition, the supporter barbeing fixed to a rotating shaft 2, and a magnetic'brush element 4 formedby collection of iron-powder carriers adsorbed to the magnets 1. Inassociation with the magnetic brushes, a pair of stirring brushes 5 arerotatably mounted, each consisting of a rotating shaft 6, an insulatedhub 7 fixed thereto, and a flexible card clothing wound around andsecured to the hub 7 and having, planted thereon, a large number ofstrong bristles of fine steel wires, hereinafter called insulated brush.The insulated brushes are mostly immersed into a developing agentconsisting of a mixture in appropriate proportion of iron-powder carrierand toner powder for generating electrostatic charge of requisitepolarity by friction with the iron powder and the insulated brushes. Thedeveloping agent is received in a reservoir 9 formed by non-magneticmaterial. In continuation with the reservoir 9, a storeroom 10 isformed, with a non-magnetic partition wall disposed therebetween partly,and receives therein toner powder 11 for supplementary use. Thestoreroom 10 has a side wall partly formed by transparent material.Within the storeroom 10, coarse steelwire brushes 12 are rotatablymounted for dispersing supplementary toner 11 that is apt to coagulatetogether. Between the storeroom 10 and the reservoir 9, a rotating steelwire brush 13 is disposed, and is consisting of a rotating shaft andfine steel wires closely planted thereon, for controlling feed ofsupplementary toner 11 to the developing agent 8. The brush 13 ishereinafter called supplementary brush. An electrostatic recordingcarrier 14 passes on the magnetic brushes 4 in light contact therewithin the direction of arrow. The recording carrier 14 has, on its lowersurface, electrostatic images 15 imparted thereto by an electrostaticimage forming device, not shown, and the images as shown by 16 aredeveloped by the developing apparatus.

The first one of features of the present invention is the shape andarrangement of permanent magnets 1, The magnetic flux of each permanentmagnet 1 before adsorption thereto of iron-powder carrier exists alsowithin the non-magnetic hexagonal supporter bar 3, but after themagnetic brush 4 is formed by adsorption thereto of ironpowder carrier,the magnetic flux of permanent magnet 1 is wholly concentratedsubstantially outside the permanent magnet, because of the fact that themagnet brush 4 is of ferromagnetic material with very low magneticresistance, while the supporter bar 3 is non-magnetic. Little leakageflux may exist in the supporter bar 3, but the magnetic force whollycontributes to the formation of magnetic brush 4 with least or no vain.According to the present invention, the permanent magnets 1 are soarranged that the adjacent magnets 1 have their same poles in oppositionto each other. If the adjacent magnets 1 should be disposed with theiropposite poles in opposition, that is, contrary to the presentinvention, magnetic flux extending remotely from the magnets to theoutside space would be remarkably decreased, even though there is littleflux in the supporter bar 3, resulting in short and hard magnetic brushin the neighbourhood only of magnet poles. According to the presentinvention, however, long and large flexible magnetic brush 4 is formedall around the series of permanent magnets 1 as shown in FIG. 1. Ourexperiments have shown that permanent magnets arranged in any mannerother than our invention result in far poor magnetic brush, unless farstrong and consequently extremely uneconomical permanent magnets areused than ours.

From the economical point of view, permanent magnets 1 used in thepresent invention should preferably be anisotropic ferrite magnets ofhigh coercive magnetic force with little fear of being demagnetizedduring treatment, which are, after magnetization, suitably combinedtogether and arranged in a required outline. The size of permanentmagnets 1 should be such that the length (length between poles) is about15 to 25 mm. and the thickness is about one third of the length, forobtaining the most large effective magnetic field. Without to say, thewidth of permanent magnet 1 should be determined according to the widthof images to be developed. The spacing between adjacent permanentmagnets 11 should preferably be about 2 to mm. In one example, permanentmagnets 1 were made from anisotropic ferrite magnets manufactured byTohoku Metal Industry Co., having magnetic strength of about 3000gausses in closed magnetic circuit, and the above-mentioned dimensionalrelation. Reduced iron powder of about IOO-mesh particle size wereadsorbed to the permanent magnets, and we obtained extremelysatisfactory and soft magnetic brush elements 4 of about 20 mm.thickness. In this example, a hexagonal hub 3 was used, but other evennumber orthopolygonal hub may also be used. Alternatively, permanentmagnets 1 of arcua-te shape may be employed and arranged on a round-barhub 3. The absolute condition is that adjacent magnets 1 should bearranged to have the same poles in opposition.

The second feature of the present invention is in the effect ofinsulated brushes 5. The insulated brush 5 is in deep intersection withthe magnetic brush 4 and mostly immersed into the developing agent 8.During the rotations of magnetic brush 4 and insulated brush 5, themagnetic brush 4 is pressed down and hardened by the recording carrier14 to be developed, but upon commencement of intersection with theinsulated brush 5, the hardened magnetic brush 4 is partly scraped downby the insulated brush 5, and partly combed thereby to be softened. Thescraped portion of the magnetic brush 4 is supplemented by developingagent 3 adsorbed to the permanent magnets 1 during intersection with theinsulated brush 5, and combed, evenly soft magnetic brush 4 isre-formed. The rotation of insulated brush 5 in the developing agent 8accomplishes commingling of ironpowder carrier and toner, and in thisprocess, the peculiar charging and carrying actions of the insulatedbrush 5 are effected. When the developing agent 8 was first charged intothe reservoir 9, it is a mixture of iron-powder carrier and toner inappropriate proportion, but the mixture is not necessarily uniform andcharging states of iron powder and toner are unstable. The rotation ofinsulated brush 5 in the developing agent 8 in such a condition causesto take place frictional movement therebetween. The iron powder andtoner, as well as the insulated brush 5, are so selected and co-relatedthat electrostatic charge produced by friction is of the same polarityin the iron powder and insulated brush 5, and of the opposite polarityin the toner, and consequently, the rotation of insulated brush 5 causesiron powder and toner to be increasingly charged in opposite polaritiesto attract to each other, while steel wires of the insulated brush 5,being insulated from each other, accumulate charge of polarity oppositeto that of toner, to increase the absolute value of their potential, forhaving toner of the opposite polarity adsorbed thereto increasingly. Onthe other hand, the magnetic brush 4 as first formed is of iron powderonly with no toner carried, but along with the rotation of insulatedbrush 5 to comb the magnetic brush 4, friction takes place between themagnetic brush 4 and the toner adhering to the insulated brush 5, andthe iron powder is charged thereby in the opposite polarity to thetoner, whereby the toner having been adsorbed weakly to the othermostportion of insulated brush 5 is partly transferred and adsorbed to themagnetic brush 4 by virtue of attracting force of the magnetic brush 4which is stronger than that of the insulated brush 5. As the rotationsof magnetic brush 4 and insulated brush 5 are continued, theabovedescribed charging and carrying actions are repeated, and eachparticle of iron powder on the magnetic brush becomes completely coveredby charged toner to obtain ample concentration of toner thereon forenabling the development of latent images on the recording carrier 14.The toner concentration of magnetic brush 4 increases promptly alongwith the rotations of magnetic brush 4 and insulated brush 5, until eachiron particle has been covered completely by charged toner, but afterthen, it becomes saturated, so that the upper limit of its concentrationrequired for development is not exceeded, even when the concentration oftoner in the developing agent 8 is very high, While the amount of tonerconsumed by developing is promptly supplemented by the insulated brush5. Thus, the requisite range of toner concentration for developing iskept without fail, provided that toner in the developing agent 8 is notdecreased below a requisite concentration therein, and yet, excess freetoner is completely prevented from attaching to the magnetic brush 4,contrary to conventional ones. This is one of the important features ofthe present invention, and enables development of long length ofrecording carrier webs and large number of recording carrier sheets tobe effected continuously in homogeneous and satisfactory manner withleast fogging contamination, provided that the initial concentration oftoner in the developing agent 8 is raised to the upper limit; thedeveloping operation can be continued without supplementing toner untilits concentration lowers to the lower limit. Consequently, extremelydelicate and difficult, continuous feed of toner as required in theconventional art is not necessary. Thus, according to the invention,toner may be supplemented intermittently and in light-hearted manner formaintaining the toner concentration in developing agent 8 above thepredetermined lower limit. Even when continuous feed of toner isdesired, its regulation is very easy and can be accomplished byremarkably simple control device.

The above-described charging and carrying effects can be accomplishedonly by so selecting elementary bristle wires of the insulated brush 5that the wires are frictionally charged to the polarity opposite totoner, and by completely insulating the wires from the rotating shaftthereof to have the electrostatic capacity of each wire as low aspossible. If bristle wires of the insulated brush 5 should be planteddirect on the rotating shaft in conductive manner, electric charge wouldnot be accumulated in each bristle wire, so that toner may not adhere tothe wires sufficiently to accomplish the intended purpose.

As a practical example, steel wires of 0.35 mm. in diameter and 15 mm.in length, each, were planted on a flexible card clothing with a densityof one wire per 20 sq. mm., and the card closing was wound around arotating shaft with a phenol-resin sleeve insulating them from eachother, so that the finished outer diameter of the brush becomes 60 mm.Such insulated brushes 5 were combined with the aforementioned magneticbrushes 4. The developing agent 8 was formed by reduced iron powder ofabout 100-mesh particle size mixed with 15 weight percent of toner ofaverage particle size of about 5 microns, which toner was made from 90parts of Piccolastic 385A resin manufactured by Pennsylvania ChemicalCo. and 10 parts of Seast Sharp 116 Carbon Black manufactured by TokaiElectrode Co., thermally fused and mixed together, and after cooling,pulverized. The magnetic brushes 4 and the insulating brushes 5 wererotated at speeds of about two revolutions and one revolution persecond, respectively, in the directions of arrows as shown in FIG. 1,and a wide and long web of recording carrier 14 running at a speed ofabout 25 meters per minute was continuously developed over 500 meterslength, without supplementing toner at all. Images thus developed wereextremely homogeneous and clear. The developed toner-powder images werefused to the recording carrier web to obtain visible permanent images,by means of preliminary conduction heating and finishing radiationheating.

The third feature of the present invention is in the toner feedingarrangement. Toner 11 in the storeroom 10 is extraordinarily apt tocoagulate, but by continuous rotation of steel brushes 12, the toner isfinely divided and carried to the feed brush 13 along the wall surfaceof storeroom 10. During such movement of toner, it is electricallycharged by virtue of friction, and its division is further facilitated.The feed brush 13 has steel bristle wires planted closely and is inshallow intersection with an insulated brush 5, so that supplementalcommingling of toner into developing agent 8 may be regulated at will becontrolling its amount of rotation. The toner that has entered into thereservoir 9 out of the feed brush 13 is promptly dispersed into thedeveloping agent 8 in the reservoir 9 by means of insulated brushes 5.As hereinbefore described, the toner concentration of magnetic brushes 4becomes saturated state by virtue of the charging and carrying elfectsof insulated brushes 5, and consequently, steel-wire brushes 12 and 13may either be rotated intermittently or continuously, for accomplishingenough the purpose of toner feeding. Since the side wall of storeroom 10is partly made transparent, toner consumption can readily be observed bysight judgment, and supplementary toner may be supplied into thestoreroom 10 at will very simply.

In the example above-described, magnetic brushes 4, insulated brushes 5,and steel-wire brushes 12, are respectivtly provided in pairs, but thenumber of such brushes used should be determined according to whether ornot the electrostatic latent images are of clear contrast, such asletters, whether or not intermediate tones should be reproduced, such asin photograph images, or whether developing speed is high or low.Besides the number of such brushes used, their sizes as well as rotatingspeeds should also be designed according to the above-mentioned matters.

According to the present invention, still further uniform developingeffect may be accomplished by controlling the rotating speed of magneticbrush 4 depending upon the toner concentration thereof in the manner tobe described. Referring to FIG. 2, the toner concentration of magneticbrush 4 is detected by measuring the amount of optical reflectionthereof by means of a suitable transducing device 17. The electricaloutput of the latter is amplified by an amplifier 18, whose outputcontrols a speed converter 19 for controlling the change ratio of aspeed changer 20. An electric motor 21 is driven through the speedchanger 20 for rotating the magnetic brush 4 and insulated brush 5. Theamount of toner adsorbed to latent images in FIG. 1 depends, of course,upon the toner concentration of magnetic brushes 4, but experiments haveshown that the same changes also widely depending upon the rotatingspeed of magnetic brushes 4, that is to say, the extended length ofmagnetic brush 4 that has swept over each point of latent images 15. Forexample, in the embodiment hereinbefore disclosed, when the recordingcarrier 14 travels at a speed of 25 meters per minute, the ratio ofamounts of toner adsorbed to latent images 15 for 0.5-revolution and2-revolutions per second, respectively, of magneticbrush rotation, isabout 1:2 for 3 weight-percent toner concentration on magnetic brushes4, about 5:7 for 7 weight-percent toner concentration, about 14:17 for15 weight-percent toner concentration. On the other hand, the amount ofoptical reflection of magnetic brush 4 is inversely proportional to thetoner concentraton of magnetic brush 4. By utilization of these factors,as may readily be understood, development of even concentration can beobtained without fail, by so designing and arranging detector device 17,amplifier 18, speed converter 19, and speed changer 20, that magneticbrush 4 rotates at decreased speed when its toner concentration is highor increased, while it rotates at increased speed when its tonerconcentration is low or decreased. Such a method of control isparticularly effective when uniform development is required forreproduction of intermediate tones, such as in photographic imagedevelopment, by appropriate adjustment of devices 17, 18 and 19, andexperiments have shown that the maximum eifect is obtained within 3-10weight-percent range of toner concentration of magnetic brush 4.

As is clear from the foregoing description, the present invention hassucceeded to utilize the effect of permanent magnet to the maximumextent, for forming long and large, flexible magnetic brushes ofcompactness, light weight, and low cost, and in their combination withcommingling, charging, carrying, and combining actions of peculiarinsulated brushes of simple construction and low cost, as well as tonersupplementing action of toner feed mechanism under extremely easycontrol, the present invention enables the magnetic brushes to bemaintained always in soft and even condition with the amount andconcentration of electric charge of toner on the magnetic brushes keptwithin a predetermined range suitable for development. Thus, accordingto the present invention, a large amount of electrostatic recordcarriers can be subjected to high speed developing operation, forobtaining clearly developed images of even concentration with leastfogging contamination.

What is claimed is:

1. An apparatus for developing electrostatic images of record,comprising a magnetic brush for development, rotating in light pressurecontact with the surface of a running electrostatic recording carrier,known per se, and an insulated brush having a large number of finernetal wires planted around a rotating shaft, said insulated brush beingin deep intersection with said magnetic brush during rotation, and alsobeing mostly immersed into developing agent in a reservoir.

2. The apparatus according to claim 1, in which said magnetic brush isformed by a plurality of permanent magnets of high coercive magneticforce arranged around a nonmagnetic even number ortho-polygonal bar,with adjacent same poles in mechanical opposition, said magnets beingrespectively disposed on and fixed to the side faces of said polygonalbar.

3. The apparatus according to claim 1, additionally comprising a tonerstoreroom connected to said reservoir, and a feed brush disposed betweensaid toner storeroom and said reservoir and rotating in shallowintersection with said insulated brush.

4. The apparatus according to claim 1, additionally comprising astoreroom for supplementing toner to said reservoir, and a tonerdividing brush rotatably mounted in said storeroom and having fine metalwires coarsely planted.

5. The apparatus according to claim 1, additionally comprising astoreroom for supplementing toner to said reservoir and dividedtherefrom by a non-magnetic partition wall, said storeroom having a sidewall partly formed by transparent material.

6. The apparatus according to claim 1, additionally comprising means fordetecting the concentration of toner held by said magnetic brush tocontrol the rotating speed of said magnetic brush.

7. An apparatus for developing electrostatic images of record,comprising a magnetic brush for development, consisting of an evennumber of permanent magnets arranged around the outer periphery of anon-magnetic supporting member, with adjacent magnets having same polesin opposition, and in equal spacings to one another, and ferromagneticpowder adhering thereto, said magnetic brush rotating in light pressurecontact with the surface of a running electrostatic recording carrier,known per se, an insulated brush consisting of tough and fine metalwires planted to and insulated from a rotating shaft, mostly immersedinto developing agent in a reservoir and in deep intersection with saidmagnetic brush during rotation, a toner storeroom connected to saidreservoir, a feed brush having tough and fine metal wires closelyplanted and rotating in shallow intersection with Cir said insulatedbrush between said reservoir and said storeroom, and a toner dividingbrush in said toner storeroom for rotation therein and having tough andfine metal wires coarsely planted, said developing agent reservoir beingformed by non-magnetic material, said toner storeroom being divided fromsaid reservoir by a non-magnetic partition wall, and said tonerstoreroom having a side wall partly formed by transparent material.

References Cited by the Examiner UNITED STATES PATENTS 2,987,037 6/1961Bolton 118637 3,103,445 9/1963 Bogdonoff et al. 1l8-637 X 3,140,1997/1964 York 118637 3,145,122 8/1964 StreZiCh 118637 3,152,924 10/1964\Vanielista et al. 118-637 3,257,224 6/1966 Jons et al l18637 X FOREIGNPATENTS 927,928 6/1963 Great Britain.

CHARLES A. WILLMUTH, Primary Examiner.

PETER FELDMAN, Assistant Examiner.

1. AN APPARATUS FOR DEVELOPING ELECTROSTATIC IMAGES OF RECORD,COMPRISING A MAGNETIC BRUSH FOR DEVELOPMENT, ROTATING IN LIGHT PRESSURECONTACT WITH THE SURFACE OF A RUNNING ELECTROSTATIC RECORDING CARRIER,KNOWN PER SE, AND AN INSULATED BRUSH HAVING A LARGE NUMBER OF FINE METALWIRES PLANTED AROUND A ROTATING SHAFT, SAID INSULATED BRUSH BEING INDEEP INTERSECTION WITH SAID MAGNETIC BRUSH DURING ROTATION, AND ALSOBEING MOSTLY IMMERSED INTO DEVELOPING AGENT IN A RESERVOIR.